Local Oedema

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  • Local oedema is the local accumulation of excess interstitial fluid.
  • Caused by disturbance of the balance betwen fluid extravasation and resorption at the level of the capillaries.
    • Outwards Forces - arteriolar
      • Vasuclar hydrostatic pressure - 35 mmHg
      • Interstitial osmotic pressure - 3 mmHg
    • Inwards forces - venular
      • Plasma protein osmotic pressure - 25 mmHg
      • Interstitial hydrostatic pressure - 4 mmHg
  • May be of inflammatory or non-inflammatory origin.

Types of Local Oedema

Inflammatory oedema

  • Generated by one or more of the following:
    1. Increased vascular permeability
    2. Increased arteriolar blood pressure
    3. Breakdown of tissue protein or transfer of plasma proteins into ECF.
      • Results in raised osmotic pressure of tissue fluid.
    4. Obstruction to lymphatic drainage.
      • Usually by fibrin.

Lymphatic oedema

  • Results in accumulation of high protein fluid.
  • May provoke a granulation or fibrous tissue response.
  • Due to:
    1. Lymphangitis/ lymphadenitis
      • Acute inflammation of lymphatics/ lymph nodes. R
      • Caused by stasis in lymphatics and/or bacterial infection.
      • E.g. “Monday Morning leg” in horses.
    2. Chronic inflammation caused by persistent or granuloma-producing bacterial infection.
    3. Tumour spread.
      • Metastasis of tumour cell plugs lymphatics and nodes
      • e.g. mammary carcinoma.
    4. Parasitic migration
      • Larvae may be following their normal pathway (e.g. Schistosomiasis), or may be aberrant.

Local venous obstruction

  • Obstruction to venous drainage may be mechanical or inflammatory-mediated.
    • Causes raised hydrostatic pressure.
    • Endothelial permeability increases due to hypoxia.
    • There may be inflammatory damage.
  • Mechanical obstruction, e.g.
  • Venous inflammation (phlebitis)
    • May be associated with thrombosis (thrombophlebitis).

"Allergic" oedema

  • Results from immediate (Type I ) or delayed (Type IV) hypersensitivity.
  • Vasular permeability is increased due to release of histamine and vaso-dilating substances.
  • E.g.
    • Insect stings (immmediate).
    • Vaccination (delayed).
    • Food reaction (delayed).

Pulmonary oedema